1. Field of the Invention
The invention relates to a stabilizing drill collar. More particularly, the drill collar of the invention is preferably octagon shaped with wear members attached to at least four, opposing sides thereof to improve exterior circulation and contact with the wall of the hole.
2. Prior Art
Stabilizing drill collars are often referred to as "square" drill collars and generally relate to essentially long length stabilizers, connectable in a drill string, used to control the rate of angle change of hole angle deviation from a desired drilling course. Use of square drill collars usually results in a smooth, gradual direction change in the hole which acts to simplify the drilling operation by preventing problems due to dog-legs, high angle deviation and reduced penetration rates. The overall effect is to produce a more usable hole at a reduced cost.
This is accomplished by a combination of drill collar body stiffness and support of the collar, by the wall of the hole, over the long wall contact length of the collar. Most square drill collars, or their facsimilies have some common, basic likenesses. All have rotary shouldered connections on each end of the collar for connecting the collar to other drill string members. All have an internal fluid flow passage extending longitudinally through the collar for drilling fluid circulation. All have designs permitting exterior fluid circulation. All have some design of hard metal, wear resistant surfaces to contact the hole wall.
A somewhat typical square drill collar is manufactured by Reamco, Inc. of Lafayette, Louisiana and is illustrated in the Composite Catalog of Oil Field Equipment & Services, 1976-77, Gulf Publishing Company, Houston, Texas, p. 4639. The Reamco "Square" drill collar is manufactured from typical steel round bar stock. The collar is termed "square" due to its appearance after ribs are welded longitudinally along its sides.
In some instances, the collar is manufactured from square steel billets that are bored for internal circulation of drilling fluids. However, the square billet type of drill collar does not provide for replaceable wear members forcing its total loss when worn to a point where it is the wrong size.
However, the basic bar stock for manufacturing drill collars is usually round. The wear members are welded onto the round bar stack to provide a replaceable wear surface that contacts the wall of the hole being drilled. Even though the finished drill collar is relieved of stress by heat treatment it has been found that welding along the length of the bar stock alters the strength characteristics of the bar stock in the vicinity of the weld. This often leads to weakening of the welded section and irreparable damage to the drill collar.
Drilco, a division of Smith International, Inc. has attempted to avoid this problem by providing an essentially round drill collar, having increased diameter sections at each end thereof and at the mid-section. These increased diameter sections are machined to receive wear pads having tungsten-carbide pressed-fit buttons, with the pads bolted in place to avoid creating a heat affected area in the collar.
All of the prior art stabilizing drill collars suffer from excessive flexibility, damage from heat affected zones and/or limited wall contact-wall support.
A primary objective of the invention is to provide a stabilizing drill collar having replaceable wear members that are welded on the collar without producing a heat affected zone that lies within the effective diameter of the drill collar.
Another objective of the invention is to provide an eight sided stabilizing drill collar having mounted upon at least four sides thereof replaceable wear members welded thereon, with the weld induced heat affected zone maintained virtually completely from the effective diameter of the drill pipe, with the drill collar having improved rigidity and wall contact.
Another objective of the invention is to provide a stabilizing drill collar having an improved exterior fluid circulation path when mounted on a drill string and placed in a well.